1. Field of the Invention
The present invention relates to a strip welding machine for butt-welding, abutting cut surfaces of a strip beginning and a strip end of metal strips to be connected. The strip welding machine includes:
a laser welding apparatus with a laser welding head;
a cutting device for producing the cut surfaces, the cutting device having cutting tools which can be lowered perpendicularly onto the two metal strips;
pairs of clamping tongues which can be moved in longitudinal direction of the strips, each pair of clamping tongues including an upper clamping tongue and a lower clamping tongue for clamping the metal strips to be connected in the region of the strip beginning and the strip end and for moving the cut surfaces together onto a support surface underneath the laser welding head until a gap-free butt joint is formed between the strip beginning and the strip end; and
pressing elements for pressing the strip beginning and the strip end against the support surface on both sides of the abutting cut surfaces.
2. Description of the Related Art
A strip welding machine of the above-described type is known from European patent 0 151 848. This known strip welding machine is preferably used in continuously operating strip processing lines. In such strip processing lines, after a coil has traveled through, the strip end thereof and the strip beginning of a new coil must be connected to each other. In the known strip welding machine, this is done by means of laser welding. Laser welding is intended to prevent the formation of projections or thickened portions in order to ensure the planeness of the metal strips even in the area of the connecting seam. However, laser welding works only if exactly parallel and plane cut surfaces and virtually gap-free abutting cut surfaces are available for the welding process. These requirements can hardly be met by the known strip-welding machine. This is because the cutting tools for the cut surface at the strip beginning and the cut surface at the strip end are combined and together form essentially a single punching unit as the cutting device. Consequently, the cut surfaces at the strip beginning and the strip end are always produced in a single punching or cutting stroke. However, it has been found that such a cutting process results in dimensional defects at the cut edges because of the occurring edge peeling, as well as crack and burr formation. As a result, the cut surfaces are not sufficiently parallel and plane for problem-free laser welding. This poor quality of the cut surfaces leads to defective welding seams.